This invention relates generally to refrigerators and, more particularly, to a method and apparatus for controlling refrigeration defrost cycles.
Known frost free refrigerators include a refrigeration defrost system to limit frost buildup on evaporator coils. Conventionally, an electromechanical timer is used to energize a defrost heater after a pre-determined run time of the refrigerator compressor to melt frost buildup on the evaporator coils. To prevent overheating of the freezer compartment during defrost operations when the heater is energized, in at least one type of defrost system the compartment is pre-chilled. After defrost, the compressor is typically run for a predetermined time to lower the evaporator temperature and prevent food spoilage in the refrigerator and/or fresh food compartments of a refrigeration appliance.
Such timer-based defrost systems, however are not as energy efficient as desired. For instance, they tend to operate regardless of whether ice or frost is initially present, and they often pre-chill the freezer compartment regardless of initial compartment temperature. In addition, the defrost heater is typically energized without temperature regulation in the freezer compartment, and the compressor typically runs after a defrost cycle regardless of the compartment temperature. Such open loop defrost control systems, and the accompanying inefficiencies are undesirable in light of increasing energy efficiency requirements.
Recognizing the limitations of such timer-based defrost systems, efforts have been made to provide adaptive defrost systems employing limited feedback, such as door openings and compressor and evaporator conditions, for improved energy efficiency of defrost cycles. As such, unnecessary defrost cycles are avoided and the defrost heater is cycled on and only as necessary, such as until the evaporator reaches a fixed termination temperature. See, for example, U.S. Pat. No. 4,528,821. However, achieving some defrost goals, such as melting all of the frost off of the evaporator and melting ice out of an icemaker fill tube, are detrimental to achieving other defrost goals, such as maintaining freezer compartment temperatures at sufficient levels during defrost operations to prevent freezer burn and moisture formation/ice buildup in the freezer compartment. Known defrost systems have not resolved these difficulties.
In one aspect, a method for defrosting an evaporator of a refrigeration system, the method utilizing a defrost heater and a controller operatively connected to the evaporator and a defrost heater, is provided. The method comprises initiating a defrost cycle to energize the defrost heater to defrost the evaporator, monitoring a temperature of the evaporator, terminating the defrost cycle by de-energizing the defrost heater when a low temperature termination point of the evaporator is reached when in a low temperature defrost cycle, and terminating the defrost cycle by de-energizing the defrost heater when a high temperature termination point of the evaporator is reached when in a high temperature defrost cycle.
In another aspect, a method for defrosting a refrigeration unit including an evaporator, a defrost heater, and a controller operatively connected to the evaporator and the defrost heater is provided. The controller includes a defrost counter, and the method comprises initiating a defrost cycle to energize the defrost heater to defrost the evaporator, selecting a low temperature defrost cycle when the defrost counter is less than a predetermined value, and selecting a high temperature defrost cycle when the defrost counter equals said predetermined value.
In still another aspect, a method for defrosting a refrigerator including a sealed system, an evaporator, a defrost heater, and a controller operatively connected to the evaporator and a defrost heater is provided. The controller includes a defrost counter and a defrost timer. The method comprises initiating a defrost cycle to energize the defrost heater to defrost the evaporator, selecting a low temperature defrost cycle when the defrost counter is less than a predetermined value, selecting a high temperature defrost cycle when the defrost counter equals the predetermined value, terminating the low temperature defrost cycle by de-energizing the defrost heater when a first temperature termination point of the evaporator is reached when the low temperature defrost cycle is selected, terminating the high temperature defrost cycle by de-energizing the defrost heater when a second temperature termination point of the evaporator is reached when the high temperature defrost cycle is selected, the second termination temperature higher than the first termination temperature, comparing an elapsed defrost time to a reference defrost time when either of the high temperature defrost and low temperature defrost are terminated, selecting a normal or abnormal defrost interval based upon the compared elapsed defrost time and reference defrost time, and operating the sealed system for the selected defrost interval.
In still another aspect, a refrigeration defrost unit for an evaporator is provided. The defrost unit comprises a defrost heater, a controller operatively coupled to said defrost heater, and a thermistor adapted for sensing a temperature of the evaporator. The controller is configured to operate said defrost heater in a low temperature defrost mode de-energizing said defrost heater at a first temperature in response to said thermistor, and to operate said defrost heater in a high temperature defrost mode de-energizing said defrost heater at a second temperature in response to said thermistor, said second temperature higher than said first temperature.
In another aspect a refrigeration unit is provided that comprises a compressor, an evaporator, a defrost heater, and a controller. The controller is operatively coupled to said compressor, said evaporator and said defrost heater, and the controller comprises a defrost timer and operates said compressor in a normal mode and an abnormal load in response to a value of the defrost timer. The controller further comprises a defrost counter and operates said defrost heater in a high temperature defrost mode and a low temperature defrost mode based upon a value of said counter.
In a further aspect a refrigerator is provided which comprises a cabinet defining at least one refrigeration compartment, a sealed system for cooling said at least one refrigeration compartment, a defrost heater, and a controller operatively coupled to said sealed system and to the defrost heater. The controller is configured to adaptively control said defrost heater and said sealed system in a high temperature defrost mode and a low temperature defrost mode between normal and abnormal defrost intervals.